Compose Key, the way to type "other charchters" in English keyboard

In order to type Ó, ö, etc, with the Enlgish keyboard, need to configure the compose key in Linux.

After this, Press "Left Window Key > " > a "  will show  ä with using only English keyboard in Linux. 

Here is some example list:

Composition key + , > c      : ç
Composition key + " > o{a,u} : ö{ä,ü}
Composition key + a > a      : å
Composition key + e > =      : €
Composition key + / > u      : µ
Composition key + s > s      : ß

And good complete references are

* http://fsymbols.com/keyboard/linux/compose/

* https://cyberborean.wordpress.com/2008/01/06/compose-key-magic/